A variety of products of a bacterial composition are commercially available for use in improving performance in biological wastewater treatment facilities. In order to be practical for application, each of these products must be provided with a shelf life through some means. Most of the products are freeze dried. These freeze dried products are dormant in the dry state, and require reactivation in aqueous media prior to addition to wastewater. Other products are liquid suspensions. Liquid products require the addition of an inhibitor at a concentration sufficient to confer self life. When the liquid suspension with chemical inhibitor is added to wastewater, dilution occurs which lowers the concentration of the inhibitor below that required for dormancy of the bacteria. Once the level of inhibitor is diluted to below the minimum level required, the bacteria reactivate, metabolize, and grow. The liquid suspension inhibited as above has an advantage over the freeze-dried product since no separate reactivation stage is required. One simply adds the liquid suspension to the media requiring treatment.
A key consideration for either freeze dried or liquid bacterial preparations is the time lag between addition to the wastewater and subsequent release of inhibition and resumed growth.
For the liquid product, release of inhibition begins with addition to wastewater. For flow-through systems, in which the detention time of any material added to the system may be a matter of hours, a short time lag before reactivation is absolutely necessary.
U.S. Pat. No. 3,963,576 of Horsfall, et al. is directed to an inhibitor for a liquid bacterial suspension and discusses the use of sulfides of sodium or potassium for this purpose.
The present invention is directed to the use of an inhibitor that confers a useful shelf life, but also provides a reactivation time which is approximately one half of the time associated with similar sulfide inhibited systems, providing a substantial advantage in systems with short detention times.